When Worlds Collide
by Doombot
Summary: What if it turns out that the world of Avatar is actually a planet in the Warhammer 40k universe, protected by Warp Storms? Now those storms have faded... and the Tyranids have come!
1. Chapter 1: The Swarm has come

_Author's Note: This takes place after the season 2 finale, but before the Day of the Black Sun. Zuko is still in the Fire Nation at the time._

Azula pointed two fingers at the gaunt horde before her, and a stream of fire shot out, killing five of them. The others rapidly responded, opening up with their fleshborer guns. Azula jumped and twisted to avoid the deadly streams of living ammunition flying at her. One stray shot hit a Fire Nation soldier further up the path, and he screamed as he was eaten alive by the deadly bugs.

"Damn," thought Azula, "That doesn't leave me with much. It's just me and fifteen soldiers facing hundreds of these things. It's time to go." She shouted, "Retreat, everybody out. Fall back to the defensive positions at the rim." The soldiers launched a final stream of fire at the gaunts, killing a few, before turning and fleeing up the path to the entrenched positions at the top of the volcano. Azula was at the head of them. They had been attempting to hold about halfway up the path. A group of soldiers stationed further up helped them, raining fire on the pursuing gaunts and killing the ones in the lead. The small party managed to reach the entrenched soldiers and armored tanks further up the volcano that housed the Fire Nation's capital city. Two of the tanks rolled forward to cover their escape. Fleshborer fire uselessly bounced off of them as they blasted the gaunts with flame. Dozens died to the fire or were simply crushed beneath the armored vehicles. Acting as one, the gaunts suddenly turned and retreated back down to the lower volcano path, stopping once they had gotten out of the range of the Firebenders.

"Are you alright princess?" asked the captain of the entrenched soldiers after Azula's party had made it to safety.

"Fine," she snapped, "Now get these men into your fortifications, I must speak with my father at once.

He bowed. "Of course, princess." And hurried off to do her bidding.

Azula sighed as she walked towards the palace. Only a month ago, she reflected, the Fire Nation had seemed invincible, with her personal conquest of Ba Sing Se and the apparent death of the Avatar (she had her doubts about that, but had far bigger problems at the moment). Then, these… these _things_ had rained down from the sky. There were thousands of them. Millions. They had rapidly lost all contact with their colonies and conquests in the Earth Kingdom, although that was because the ones with wings had simply eaten the messenger hawks almost as soon as they left, so no one knew what was going on over there or if any forces were still holding out. Soon after, several islands had been silenced as well, and soon the swarm was on the very capital itself. They had taken the outer defenses and the harbor, but the Fire Nation still held the upper volcano and the main part of the capital city inside of it. Any and all able-bodied civilians had been conscripted into the defense force, as had all law enforcement officers. They had mustered some 5,000 regular troops, with an addition 13,000 militia (what the conscripts were called), and 150 armored vehicles to defend their capital. They faced what seemed an innumerable horde, although they did know a bit more about them now. For one thing, the bigger creatures seemed to be some types of leader. If they were killed, the smaller ones would lose all of their normal eerie cohesion and scatter until another large creature came along. Killing them seemed to be the key to victory. Unfortunately, they were two-story armored killing machines, so this was easier said than done.

Azula and her original 40 soldiers had been sent on a mission to take out a particularly large specimen that that participated in the attack on the harbor. She had succeeded, melting its head with a bolt of lightning, but at the price of 2/3 of her squad. These were drawn from the best soldiers they had available, and were certainly not replaceable. They needed every man they could get. After the large creature was killed the swarm around it had wavered and scattered, but then another monstrosity (albeit a good deal smaller than the dead one) had shown up and rallied them. Dozens of the smaller creatures had died to a massive coordinated fire blast from Azula and her squad, but the large beast had charged them, killing a dozen Fire Nation soldiers by itself, and forcing the rest to fall back to the volcano. From what Azula could see, the remaining large creatures were having difficulty keeping all the smaller ones in range of whatever strange ability they used to control them. There weren't many of them left as the Fire Nation defenders had targeted them throughout the battle as ordered, but it still didn't look good. All they had to do was get the thousands of smaller creatures to charge the defenses and they would undoubtedly be overwhelmed. She moved a little faster towards the palace at that thought. She had to get her father to turn over the armored units to her. She knew the smaller creatures couldn't hurt them, only the larger ones. Her plan was to remove them from the defensive perimeter and have them launch a rapid assault at the creatures gathering at the base of the volcano. They needed to take out the enough bigger creatures to make the swarm lose all coherence. Then they could retake the rest of the island and mop up any remaining small creatures. It would be simple enough to kill them without the larger ones to guide them, Azula knew. It was a risky plan, though. She had seen what the large creatures could do to tanks if they got close enough, their claws ripping through armor like wet paper. Really, it only had a slim chance of working. On the other hand, if they were to sit there and attempt to hold out, sheer numbers would overwhelm them and they would all die. A slim chance was better than none. Azula broke into a run.


	2. Chapter 2: The Battle begins

Azula sprinted towards the palace as fast as her legs would carry her. She knew that they didn't have much time until they were completely overwhelmed. Unfortunately for her, her father had taken overall command of the capital's military units, and even she couldn't override their current mission without his express authorization. She watched as about a dozen flying creatures swooped overhead, clearly scouting their numbers and position. A few soldiers attempted to blast them with fire. One of them got a lucky shot, catching the creature on the wing. It let out a ghastly shriek and plunged to its doom. Azula hurried on.

She ignored anyone in her way, and simply jumped right over the soldiers guarding defensive fortifications deeper in the capital. As she reached the palace, the guards in front, seeing that she was in a hurry, opened the enormous ceremonial doors for her. She shot in, weaving her way down the hall into the council room. She burst through the door, panting heavily. Her father and his accompanying generals all looked up from the map on the table and stared at her.

"Azula," Ozai said calmly "did you succeed? Is that monstrosity dead?"

"Yes," Azula managed, struggling to catch her breath "But there are several more, and they've already regrouped most of the smaller creatures. It won't be long before they strike."

"We were just discussing that. We feel that we have a reasonable chance of beating them off if we simply remain here."

"No," said Azula "You haven't seen just how many are out there. Tens of thousands. Maybe hundreds. They have enough troops to bury us under the weight of their own dead. Our only chance of survival is to strike hard and fast, right now, with all our offensive power. If we can take out enough of the big ones before they can rally all their troops, the whole swarm will lose cohesion and collapse. Then we can hunt down the smaller creatures at our leisure. If we hang back and try to dig in, the larger ones will simply send wave after wave of their cannon fodder at us until we're overwhelmed. We won't be able to defeat an army that size in a war of attrition."

"I see," muttered Ozai thoughtfully "And what is your recommendation then? If we cannot defeat these creatures from dug in fortifications, how will charging them help us?"

"We've got to take our remaining tanks and try to kill enough of the big ones right now, while they're not done organizing their troops. If we succeed, we've won."

"And if we fail then our defenses are weakened considerably. May I remind you that many of the tanks are forming crucial parts of our hastily-constructed lines? Or that these creatures have difficulty destroying them? The larger ones are the only ones we've seen thus far with the strength to cut through armor. Why risk our lines when the larger ones must come to the tanks anyway?"

"Because they'll be able to take on the tanks one at a time, when they don't stand a chance. They can just cut a few holes in our lines, and then their troops can pour in and crush us all. Then they can pick off whatever tanks are left at their leisure. The monstrosities can easily defeat a tank in one-on-one combat. It's only in a group that the tanks stand any chance at all. We have to concentrate them to have a hope of winning."

"I see. And I presume that you would want to command this attack."

"Yes. Please make your decision quickly. We don't have much time, and our window of opportunity is closing rapidly. I need to get this moving as soon as possible."

"Hmmm…" Ozai appeared to be mulling it over before he said, "Very well Azula, but do not fail me in this. It would be better for you not to come back at all than to come back in failure."

Azula knew he meant it.

Azula climbed into her chosen armored vehicle. She was to lead the attack from inside one of the initial vehicles in the charge. She looked out the viewport and paused briefly before loosing a blast of blue flame skywards. That was the signal. Over a hundred tanks surged forward in almost perfect unison. Azula actually felt confident that her plan might work. She watched as the initial vehicles disappeared over the ledge of the volcano and started down the path. Then her vehicle crossed it and she saw what was below. In an instant, all her confidence evaporated. There, at the volcano's base, was a horde too numerous to count. Hundreds of thousands of creatures swarmed the ruined lower city and docks. Azula was not normally a particularly religious person, but at that moment she said a silent prayer to Agni. Of course, she let no look of fear cross her face, knowing that to do so would be disastrous for morale. She looked more closely at the horde, and felt partially relieved. It was clear that the number of creatures was making it very difficult for the larger ones to bring the smaller ones into range of whatever strange ability they had that allowed them to control the horde. There only seemed to be about thirty-five of the larger creatures, and they were having to call the smaller ones into very tight bunches around them to keep them under control. That, in turn made it difficult for them to move. Even as she watched, one of them toppled over, crushing many of the smaller creatures surrounding it as it crashed. She had to resist the urge to laugh. The enormous thing, however, seemed unharmed and rapidly got to its feet. It and the swarm moved as one, and more of the smaller creatures closest to it ran to join the group. By now the vanguard tank force was approaching the bottom, with the swarm seemingly too busy to notice them. Azula knew that wouldn't last long. Gathering all her power, she loosed a bolt of lightning at the nearest big one. All tanks in range loosed fire at the swarm. The battle had begun.


End file.
